Menus: make it possible to have items with different height

Can be usefull for separator
(Required for slint-ui#8339)

Author: ogoffart

internal/compiler/widgets/common/menus.slint

@@ -9,6 +9,8 @@ export component PopupMenuImpl inherits Window {
     in property <[MenuEntry]> entries: [];
 
     property <int> current-highlight: -1;
+    // `y` position of the currently highlighted menu entry
+    property <length> current-highlight-y-pos;
     property <int> current-open: -1;
     property <length> px: 1rem / 14;
 
@@ -25,6 +27,12 @@ export component PopupMenuImpl inherits Window {
                 entry: entry;
                 is-current: current-highlight == index;
 
+                changed is-current => {
+                    if self.is-current {
+                        current-highlight-y-pos = self.absolute-position.y - root.absolute-position.y;
+                    }
+                }
+
                 set-current => {
                     focus-scope.focus();
                     root.current-highlight = index;
@@ -50,7 +58,7 @@ export component PopupMenuImpl inherits Window {
 
                 if current-highlight >= 0 {
                     if entries[current-highlight].has-sub-menu {
-                        activate(entries[current-highlight], y-pos(current-highlight), current-highlight);
+                        activate(entries[current-highlight], current-highlight-y-pos, current-highlight);
                     } else {
                         current-open = -1;
                         sub-menu.close();
@@ -59,10 +67,6 @@ export component PopupMenuImpl inherits Window {
             }
         }
 
-        function y-pos(idx: int) -> length {
-            frame.padding + idx * (frame.height - 2 * frame.padding) / entries.length
-        }
-
         key-pressed(event) => {
             open-sub-menu-after-timeout.running = false;
 
@@ -86,12 +90,12 @@ export component PopupMenuImpl inherits Window {
                 return accept;
             } else if event.text == Key.Return {
                 if current-highlight >= 0 && current-highlight < entries.length && entries[current-highlight].enabled {
-                    activate(entries[current-highlight], y-pos(current-highlight), current-highlight);
+                    activate(entries[current-highlight], current-highlight-y-pos, current-highlight);
                 }
                 return accept;
             } else if event.text == Key.RightArrow {
                 if current-highlight >= 0 && current-highlight < entries.length && entries[current-highlight].has-sub-menu && entries[current-highlight].enabled {
-                    activate(entries[current-highlight], y-pos(current-highlight), current-highlight);
+                    activate(entries[current-highlight], current-highlight-y-pos, current-highlight);
                 }
                 return accept;
             } else if event.text == Key.LeftArrow {